Multichannel electrical pulse communication system



July 10, 1951 A. H. REEVES 2,559,661

MULTICHANNEL ELECTRICAL PULSE COMMUNICATION SYSTEM Filed April 2, 1947 4 Sheets-Sheet l FIG.|.

FIG; 2.

INVENTOR. 'ALEC HARLEY REEVES ATTORNEY A. H. REEVES July 10, 1951 MULTICHANNEL ELECTRICAL PULSE COMMUNICATION SYSTEM Filed April 2, 1947 4 Sheets-Sheet 2 INVENTOR.

s E V E E R Y E L R A H C u ATTORNEY y 1951 A. H. REEVES 2,559,661

MULTICHANNEL ELECTRICAL PULSE COMMUNICATION SYSTEM FIG 4 IN VEN TOR.

ALEC HARLEY REEVES BY ATTORNEY July 10, 195] REEVES 2,559,661

MULTICHANNEL ELECTRICAL PULSE COMMUNICATION SYSTEM Filed April 2, 1947 4 Sheets-Sheet 4 Li i T 89 90 35 a III FIG.6.

INVENTOR. ALEC HARLEY REEVES A TTORNEY Patented July 10, 1951 UNITED STATES PATE Q FWE MULTICHANNEL ELECTRICAL PULSE COMMUNICATION SYSTEM Alec Harley Reeves, London, E gland, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of'Delaware Application April 2, 1947, Serial'No. 738,954

12 Claims.

Thisinvention relates to a multichannel com- I munication system. More particularly it, deals with a system for modulating pulses .by signals and rearranging the repetition periods of these pulses to reduce interference between pulses of different signal channels.

The principles of modulating pulses by signals have been described in detail in the U. S. Patents Nos. 2,262,838 and 2,266,401, as Well as several copending applications. patents it is not necessaryto transmit the variations in amplitude of a signal continuously but it is sufiicient to send discrete pulses, representing amplitude values, spaced at intervals not longer than about /3 of the period of the highest signal frequency to be transmitted. These amplitude values may be transmitted as amplitude modulated pulses, frequency modulated pulses, or time modulated pulses. Since it is sufficient to send only a small fraction of each signal the space between the pulses representing this fraction' of the signals may be interleavedwith pulses of other signals to produce a multichannel pulse wave. If the pulsesof different signal channels are interleaved in time too close to each other, interference between the pulses of different channels will occur and produce what is known as crossgtalk. Accordingly, it is the purpose of this invention to rearrange the pulses of different signal channels on a multichannel pulse wave so as to reduce this cross-talk This is accomplished by grouping pulses of the same channel together and j increasing the time spacing between these groups. Then after transmission and reception of the rearranged pulses, the groups are separated and the pulses comprising them are re spaced according to their original spacing for demodulation. In performing this function of rearranging the pulses, it has been found that a much cross-talk ratio may be tolerated between the pulses in a given group than can be tolerated between the interleaved pulses of the adjacent different signal channel pulses. This re-arrange.- ment permits a closer grouping or time spacing of the pulses within a group thereby increasing the available time spaces for pulses otothersignal channels on the same carrier waveor medium without substantial increase in the width of the carrier wave frequency band.

Accordingly, it is an object of this invention to provide a novel and effective modulatedpulse niulti-channel communication system.

7 Another object is to reduce the interference =be'twee1r channels in a modulated'pulse multichannel communication system, which inthecase As explained in these 2 of .audio signals is commonly referred to as cross talk.

Another object is to increase the number oi .difierent signal channels which may be trans; mitted on modulated puls o e a given ,Qi-re quency band width.

Another object is. to reduce thecross talktor a given bandwidth, or to use a reater bandwidth for a given cross-talk.

Another. object is to provid a nqrel nd. f cr time. distribution and delay m ans. f r ar 5-? ing .the pulses in a multichannel commun cation system.

Another. object is to provide noveland effective means forseparating and demodulating the mod ulated. pulses rearranged according to the. multifchannel communication system Of this invention.

Stillother objects. will-ap ear rgm time to time in the description which follos.

ypeaking, the essential :featu se th modulated pulse multichannel communic t on system of. this invention CQmDli QS (l) means ra ge the time spacing of .a given number of pulses in each of .the trains of different signal modulated pulses toproduce trains of regularly recurring groups of modulated pulses; (.2) means, to. interleave these groupspf pulses oi these diflerent pulse trains to form asing-lemultbchannel pulse wave; (3) means to transmitthemu 1: channel pulse wave; (4) means to receive, e multi-channel. pulse wave; and v.(5) means..-;to rearrange and/or. separatev the groups 101? puls of the multichannelpulse Wave toreproduce the original pulse trains which may be, demodulated accordingto any of the known pulse. .demoduia-t: ing procedures.

As disclosed. in .the above-mentionedpatents the signals or each difierentchannel to be tr..- t y the systeml i this invention medu ete pulsesat a. regularly recurring :rate- In order 1119 facilitate rearrangerrient of the pulse aces). g to the system of this invention and tcjpre undue. interference, the repetition rates of the pulses .of. the ,;differ.ent}5i .a1 chan els oul be the same or, should be even multiples of each other. This. is accompli hed by sy chmmzin thepulse modulators for each, of the al channels with the same or ide tica Sin c oni naci cuits or ba e wer enerator A given number of pulses fromthe resulting tr us of regularly and even y mep ced si na ate p lses are. thenselected-m1? earthercun rearranged. in time .spacingor bunched. R et. .1 to form attain .ofgroun nf c oselrtime area .1 pulses, which groups recur at .a re ula 3 netitlan rate. The means for rearranging these pulses into these groups comprises a network of delay devices such as a network of trigger circuits, wherein a separate and differently timed delay device is provided for each one of the pulses of the group.

In order tomix or interleave the rearranged groups of pulses of each of the separate signal channel pulse trains to produce the desired rearranged multi-channel pulsewave, a special electronic distributive device may be employed such as a cathode ray tube having a plurality of targets, one for each of the pulses in each of the difierent recurring groups of pulses. Such a cathode ray tube may take the form of a Cyclophon described in the copending application of Labin et al. (87-95) Ser. No. 565,152, filed November 25, 1944, now U. S. Patent No. 2,465,380, granted March 29, 1949, or of a Cyclodos described in copending application of Labin et al. (86-94) Ser. No. 591,065, filed April 4, 1945, now U. S. Patent No. 2,429,631, granted October 28, 1947, if time modulated pulses are employed. Instead of such an electronic mixing device, a series of channel deblocking circuits may be provided which are joined to a suitably isolated mixing circuit. This mixing circuit may comprise a series of vacuum tubes having interconnected anode circuits.

The resulting rearranged multichannel pulse wave may then be transmitted and received over any suitable medium, such as by radio or through a coaxial cable or the like. The receiver for receiving the transmitted rearranged multichannel pulse wave is designed to cooperate with the type of transmitter employed, so that the transmitted wave may be detected and reproduced without distortion, for separation of any one or more of the signal channels thereon and the demodulation of those channels. Since the time spacing of the pulses in each group is diiferent from that of time spacing of those portions of the original signal modulated pulses, the different groups of pulses must be separated from each other to produce trains of grouped pulses and these groups of pulses must again be rearranged or spread out to reproduce the original signal channel pulse trains before they are demodulated. This also may be accomplished in an electronic distributor device, such as a Cyclophon or in a suitable deblocking circuit, or a combination of both. In order to facilitate the separation of the different signal channels, a synchronizing pulse may be transmitted over one or more of the channels or group spaces on the multichannel pulse wave, which synchronizing pulse may be separated in a suitable circuit for synchronizing the electronic distributor or separating and demodulation circuits. However, the group repetition rate may be detected by suitable filter means for generating such a suitable synchronizing wave in the absence of a specific synchronizing signal.

After the trains of groups of pulses are separated from the received multichannel pulse wave, the pulses in each group may be arranged by suitable delay networks, similar to those mentioned above for grouping these pulses, wherein a separate delay device, such as a trigger circuit, is employed for each one of the pulses, having time constant circuit of the proper value for spreading the time spacing of the pulses evenly again along signal channel pulse trains. These train may then be directly passed to suitable demodulators for reproduction of the signals thereon. One advantage of employing an electronic distributor device of the Cyclophon type is that demodulation as well as separation of the pulses may be simultaneously accomplished therein as described in the above-mentioned Labin et al. application Ser. No. 565,152.

The above steps in the communication system of this invention are applicable both to electro'- magnetic and electrical wave systems as well as to acoustic or ultrasonic waves in gases, liquids or solids. Similarly, acoustic delay lines and devices may be employed in the place of the trigger circuits above-mentioned.

While the invention itself is defined in the appended claims, the foregoing and other features and objects of the invention will become more apparent and the invention best understood upon consideration of the following detailed description of an embodiment of the invention to be read in connection with the accompanying drawings in. which:

Fig. 1 is a graph of an amplitude modulated multichannel pulse wave produced according to previous multichannel pulse modulated methods;

Fig. 2 is a graph of a multichannel pulse wave showing the pulses of the wave in Fig. 1 rearranged into groups according to the system of this invention;

Fig. 3 is a schematic block wiring diagram of the system for rearranging the pulses according to the waves shown in Fig. 2;

Fig. 4 is a. schematic block wiring diagram of a system for separating the wave shown in Fig. 2 into a plurality of separate trains of signal channel pulses spaced according to those shown on the wave in Fig. 1;

Fig. 5 is a wiring diagram of two stages of a delay-device which may be employed in the circuits shown in Figs. 3 and 4;

Fig. 6 is a graph of a wave form useful in explaining part of the operation of the circuit in Fig. 5.

For the purpose of illustration the modulated pulses disclosed in Figs. 1 and 2 will be shown to be amplitude modulated according to the si nals of the ten different signal channels A, B, C, D, E, F, G, H, I and J. However, the pulses may be time modulated instead of amplitude modulated as described in the above-mentioned patents. Referring specifically to Fig. 1 the wave I represents the audio frequency wave for signal channel A and the dotted wave 2 represents the audio frequency wave for signal channel B. The other eight signal channel waves are not shown in Fig. l to avoid confusion. As previously stated, it is not necessary to transmit the variation in amplitude of waves I and 2 continuously, since discrete amplitude values at regularly spaced intervals may be transmitted and still give sufiiciently complete reproduction of the original audio frequency wave. These different amplitude values are represented by the pulses A-|, A--2, A3, A-4, A-5, etc., in Fig. l and similarly the dotted pulses Bl, 13-2, B3, etc., for signal channel B. The A pulses and the B pulses as well as the pulses of each of the other signal channels have the same repetition rate and are shown out of phase with each other so as not to cause interference for convenience and to illustrate prior multichannel pulse waves. Since the pulses do not have absolutely vertical leading and trailing edges but are wider at their base than at their peaks, overlap may occur between two successive pulses if the time spacing between Al and Bl were too small, thereby producing cross-talk in either prevent such cross-talk, 'particularlyif' adjacent pulses are of different signal channels as shown in" Fig. 1. For example, in telephony, wherein pulses of say a half or one micro-second in width or duration are employed, it has been found that no pulse should approach that pulse of another channel closer than about two and a half microseconds in general in order to pre- Vent interaction greater thanabout 60 decibels down. However, if the two adjacent pulses are of the same signal channel a'figure of about 15 decibels down is in general allowable with a spacing of about onemicrosecond without materialinterference, thereby'permitti'ng the trans; mission of about two and a half times as many channels as before over about the same frequency band width.

Thus, the pulses of each signal channel are arranged into groups of an equal number of pulses which groups contain pulses that are closely spaced in time different groups of pulses being farther apart in time than the distance between the pulses in each group as is shown"- in'the wave on Fig. 2. In this figure-the pulses- A'-|, A-I! A-HJ have been bunched together within the time space or bracketed distance '3 and similarly-pulses B-l, B2 .B| have been-bunched together within the timespace 4, etc., with the time space between each one of the groups; This isaccomplished by -delaying pulse AI substantially one complete cycle, represented by the entire length in time-- taken-up by the ten- A pulses in Fig. 1- plus the time 6 shown in Fig. 2. This consider -the point 1 onthe wave in Fig. Z'startin in time at the point of pulse Al0-in Fig. 1, and-the spacing; between pulse A-l in Fig. 1 and A-| in- Fig.- 2- to be 91- time units; the time delay between pulse A2 in Fig. 1 and A2 in Fig. 2 to be 81.9 time units; the time'units between pulse fil -3' in Fig. 1 and A 3 in Fig. 2 to be; 728;

etc. In this way allthe pulses are compressed in time into'a space of 9.1 time units, which isf less than the original time interval between adi jacent pulses of the same signal channel shown Similarly, the pulses of channel Bi may be delayed to fit in the space 4 in Fig; 2

in Fig. 1.

by adding time units to each above.- Between the'last pulse- 30f: channel A. inFig. 2 and the'firstpulse 13-! in group 4 of channel B, there is a time interval of 1.9 time units, a distinguished'between only 0.91 time unit between pulses-ofdif ferent signal channels ill-Fig.1. This increased time spacing between pulses of different chandelay illustratednels materially reduces the cross-talk betweenthem.

The number of pulses in each group is notimportant in that more or fewer than ten, such as five, may be employed if desired. However,

the smaller the number of pulses in eachgroup the less time spacing on the wave is saved for more different signal channels, sincemorelarge spacings are required between the different} groups of pulses. Similarly, for a given band width the more pulses that are in one'group' the less portions of any given signalwave may? be'transmitted in a given time, which may-tend to decrease its fidelity.

Although only one cycle ofygroups of-pulses;

are shown in Figs. 1; and 2, similar cycles of" grpup'sfof' -pulses recur along; the'wave which cyclesorgroups maybe separated" by synchro-=' termined in a properly tuned circuit from which a synchronizing wave may be generated at the receiving end of the system for synchronizing the pulse separator and demodulator circuits.

The transmitting portion of this system isschematically shown in Fig. 3 wherein the ten separate signalchannels A through J are introduced into separate pulse modulator circuits 8, eachof'which is synchronized by a common" synchronizing circuit 9 through lines Ill. The pulse modulator'circuits 8 may .-be of any known type for modulating the signals according to amplitude pulses as shown in Figs. 1 and 2, 0r according to time modulated" pulses as described'i'n the above-mentioned patents. The synchroniz ing circuit 9 may comprise a base wave generatorhavinga frequencyequal to that of the pulse repetition rate, or an even submultiple thereof. Theseparate trains of regularly recurring signal modulated pulses are separately passed through lines I-I into networks of delay devices to delay the pulses shown'in Fig. 1 to the group positions shown in Fig. 2; For each one of the 10 pulses? which: makes-up group 3 for channel A, there is provided a separate delay device l2, l3, etc., I4 corresponding to delay -2 n, whereinn is 10. From each one of these delay devices" is a line; l5; IS-l'l containing a rectifier l8and a resistance I 9 to ground. These lines I5, Iii-Il may be connected to the separate group A dynode targets 20, 2|, 22, 23, 24, 25, 26, 21', 28 and 29 having a common collector electrode 3|l-"of a cathode'ray distributing device. These targets are struck in succession by a cathode ray beam 3| controlled by deflection plates32 coupled toa sweep circuit 34 synchronized by the "synchronizing circuit 9 through lines Ill and 3 5.

The common collector Sills coupled through'line' l3; to target 2| while the next pulse A-'2 passes to target 2 8;

The time constant of the circuits connecting thepulses to the" targetsis sufiiciently short SO' as topermit the'charge produced'on each of said" targetsby a pulse to leak off before thenex'tf pulse is applied. Thus, for example, the charge of'pulse A-l leaks 01? target 26 through resi'sta-ncelll to ground before the pulse A2 is applied thereon. Similarly, other succeeding pulses.

are applied-to each one of the targets 2| to 29 and leak off; When the A-I pulse reaches target 29, the beam 3| strikes the target 29 causing secondary electrons to be emitted thereby and? co1l'ected' by collector 30;" When the beam. 3|, moves onto-strike target 28, pulse A2 is being applied'at' that time to target 28, andjthe im pings-merit of 'thebeam upon target 28. likewise thusproduping a corresponding current pulsein line 35, Succeeding pulses A 3' to A"|0 similarly reach causes electrons to flow to collector 30,

their corresponding target as the beam strikes tothe next-signal channel, B, and similarly on.

around the cathode ray device past all itshundred targets, each time striking a target at the time the corresponding pulse is applied thereto.

Similarly, the pulse grouping circuit for signal channel B comprises a series of delay devices 39, 4fl4| (corresponding to delay devices 12, I3l4) for correspondingly delaying the pulses BI, B2 .B-I before being passed through rectifiers 42 in line 43 (grounded through resistance t5) and applied to the group of targets 45 corresponding to channel B on the cathode ray distributing device. However, to prevent overlap of the pulses of group 4 with those of group 3 an additional delay means 46 is inserted in the line i I between the pulse modulator 8 for channel 13 and the series of delay devices 39,

404l. This delay device 46 is sufficient to space the group of pulses 4 a time space 5 from the last pulse A-li! in group 3 shown in Fig. 2. correspondingly, a space is provided between target 28 and the first target 45 in the cathode ray distributing device. Similarly, other delay means like 46 are inserted in lines I l for the other signal channel modulators to cause the groups of pulses to be properly spaced from each other.

Although Fig. 1 shows the pulses of the different signal channels out of phase with each other, such is not necessary in the circuit shown in Fig. 3, since the delay means 46 may be adjusted to prevent overlap of the final groups of pulses. Therefore the repetition rates of the signal modulated pulses in each line H may be the same both in frequency and phase.

The signal from the transmitter 31 shown in Fig. 3 may be transmitted by radio or over any other suitable medium and received through line 41 in a suitable receiver and detector 48 shown in Fig. 4. From the circuit 48 the received grouped or rearranged multichannel pulse wave shown in Fig. 2 is passed through lines 49 and 58 into a synchronizing circuit 5i which may comprise means for selecting synchronizing pulses (not shown on the' wave shown in Fig. 2),. or means for producing a synchronizing wave from the repetition rate of the groups of pulses thereon. The resulting synchronizing wave may be withdrawn from circuit 5i through line 52 to a sweep circuit 53 which may be employed for controlling the sweep of a cathode ray beam 54 in a cathode ray distributor device having deflecting plates 55 coupled through lines 56 to the sweep circuit 53. The grid 51 of the cathode ray device may be connected to line 49 through line 58 to control the intensity of the beam in accordance with the pulses on the wave in Fig. 2. At the target end of the cahode ray device are a series of targets 59, 69, 6|, 62, 93, 64, 65, 66, 61, 68 and others corresponding to each one of the pulses for each group along the wave shown in Fig. 2. As the cathode ray beam 54 passes each one of these targets 59 through 63 in synchronism with the location of the pulses Al, A-2 Al9 on the wave in Fig. 2 the beam 54 is intensified according to the amplitude of the pulses A-l, A2 A-lil, thus producing a proportional current flow in the form of a pulse from one of the targets 59 through 98. These pulses pass through lines 69, ill-11 containing rectifiers 12 to the delay devices 13, 14-45 (similar to delay device l2, l3, l4 shown in Fig. 1) wherein their 8. time position on channel A is again arranged to correspond to that shown in Fig. 1. These redelayed pulses are then withdrawn from the series coupled delay device 13, -'I4-'|5 through line 16 to produce a train of evenly spaced pulses. This train may then be passed to a suitable demodulator circuit, which, in the case of the amplitude modulated pulses as shown, may comprise a suitable filter TI. The resulting demodulated signal, corresponding to signal channel A, may then be withdrawn from filter 11 through line 18 as wave l in Fig. 1.

Similarly, a group of targets I9 corresponding to channel B are provided along the sweep circuit of the beam 54 in the cathode ray device; The targets 19 are coupled through lines 88 containing rectifiers 8|, to another series of delay devices 82, 83-434 (similar to 13, 14-15) from which may be withdrawn through line 85 the pulse train B-l, B'2, 3-3 B-lfl shown in Fig. 1. This train of B pulses also may be passed through a suitable demodulator or filter 86 (similar to 11) for reproduction of the signal wave 2 and withdrawn through line 81. Similarly, the other signal channels C through J have corresponding groups of ten targets around the sweep path in the cathode ray device for contact with the beam 54 to separate the separate signal channels, as well as having similar networks of delay devices for rearranging the pulses according to their original spacing and demodulating the resulting pulse trains.

Rectifiers l8 and 42 in Fig. 3 and I2 and BI in Fig. 4 are used in the lines to prevent unwanted back coupling between filter sections and between delay means.

The conventional type of passive delay network which may be used in the circuits of Figs. 3 and 4 has the advantage of simplicity and reliability against breakdown and is very flexible as to the values of delay that can be easily obtained. However, in general a slight progressive deterioration of the pulse wave form occurs as the delay sections are cascaded. If time delays 0f very short duration are employed it is also important that temperature and other such precautions be taken to ensure the needed constancy of delay time. To avoid these drawbacks in the case of time modulation systems, each delay service -I, -2 11. may consist of a vacuum trigger circuit of such design that when an incoming pulse reaches it the circuit changes from one electrical equilibrium position to another, and then restores itself to the first position after the desired predetermined delay.

One form of such a trigger circuit comprising two stages in series or cascade is shown in Fig. 5 each stage in the form of an Eccles-Jordan trigger circuit. The double triode 88 has anode resistors 89 and 99. Anode 9| is connected to the grid 92 through resistor 93 and any undesired positive bias is removed from grid 92 by series resistors 94 and 95 connected to the negative side of the battery 96. Grid 91 has grid resistors 98 and 99 in series to ground. Grid 9'! is connected to the anode I80 through condenser llll. Such a circuit with suitable constants in the absence of applied potentials will take-up a stable position such that full current flows through the anode 9|, while the grid 92 is at cut-off. On the application of a negative impulse to the grid 91 through condenser I02 from the input terminal I03, the circuit is triggered over into its second equilibrium position, in which case current flows to anode while the current to anode'SL iscuteofi. If no. further 'pulses arrive, the circuitswill then restore itself it its first equilibriumposition after a time interval depending primarily on the values of condenser I01 and resistors 98 and 99. Thisdelay time, before restoration to thefirst position, is arranged to be the value-desired for that particular delay section.

A second doubletriode I04 .is arranged in an exactly similar circuit to that of double triode 88. At the moment the circuit of the triode 88 restores itself to the equilibriumposition, the current in the anode 9I rises suddenly. The resulting negative impulse generated oniil is coupled through condensers I05 and I06. in series to the grid I07 of tube I04. The circuit of tube I04, is thus triggered to its second equilibrium position in exactl'g the .same way as the circuit of double triode 88 wastriggered by the initialincoming pulse. at terminal I03. After theprearranged delay (the delay time of this second section associated with double triode I04) the circuit of tube I 04 will return to its initial or first-equilibrium position, in the .process of which it emits a negative impulse from .theanode I08 which can be used to trigger the third section which may be coupled to line I09, if desired. In this way, any number of sections may be connected in cascade.

Although with carefuladjustment of the constants, the desired stable operation may be attained as described above the tolerances on components may be increased by the addition of a rectifier tube l-I0, which maybe either a-diode or a suitable metal rectifier having low capacity. This rectifier H shunts to the ground all positive impulses, thus preventing the possibility of back triggering of the tube 88 on the restorin pulse of tube I04. A similar rectifier tube I I I may be provided for the next stage (not shown).

With existing types of vacuum tubes, the restoring time of the circuit may be reduced to less than 2 microseconds. The speed of restoring may be speeded up still further and the circuit delay partially stabilized by the addition of a suitable steady wave applied across the terminals H2 and H3. One form of such a suitable wave is wave H in Fig. 6 which may be applied between terminal II2 and the ground terminal I I4. The form of the wave between terminals I I3 and H4, has an equal voltage to that shown in Fig. 6 but of opposite sign, and can easily be obtained by a phase inverter (not shown). Terminal H2 is connected through condenser II 6 to point II I between resistors 98 and 99, and terminal H3 is connected through condenser M8 to point II 9 between resistors 94 and 95. If we assume that all of the incoming negative pulses arrive between times I20 and IZI, or between times I 22 and I23, etc., shown in Fig. 6, the voltage at terminal II2 adds itself to the incoming negative pulses and is only operative between the desired time limits. The opposite phase of the voltage Wave applied to the point H9 on to the second. grid 92 of tube 88 produces the same effect. The amount of voltage in wave I I5 is adjusted so as not to trigger the circuit itself, but is of sufiicient value to insure the restoring time is always within the desired limits I20 and I2I, or- 22 and I23, etc. The restoring time can be reduced by this addition of the voltage to 1 microsecond or less. In this Way, the desired increased speed of operation together with stabilization of the average delay times within the required limits can be achieved provided that the fundamental frequency 0;, the

wave H5 is synchronized time. p

In the same way the wave form of Figr6-may be applied also to all, or to a desired number, of the trigger circuits in any one group. If it is applied to. all such trigger circuits, then both the speed of operation and the delay stability will be increased. If it is desired to increase the stability without increasing the speed of operation, it may be sufiicient to apply the wave only to every alternate trigger, or everythird trigger.

'While the above is a description of-the prin ciples of this invention in connecti n with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of this invention.

Iclaim: I

1. In a multiplex communication system ofthe type wherein each communication channel comprises a train of discrete pulses of substantially predetermined time spacing, a method of reducing interchannel crosstalk comprising changing the spacing of a predetermined number of pulses of each channel to provide relatively close grouping within the period of said predetermined spacing-and applying the grouped pulses .of each channel to a common transmission medium in interleaved time relationship with other such groups, with the spacing betweenieach of. said groups exceeding the changed spacing of the pulses within each group. 7

2. A multichannel communication system wherein each signal-channelis modulated on a separate. train of pulses .hav'ing.thesamepulse repetition rate comprising: separate means to group in time a given number of said pulses on each train to produce trains of regularly recurring groups of pulses, means to interleave said groups of difierent pulse trains with each other to form a multichannel pulse wave with the pacing between each of said groups exceeding the spacing of the pulses within each group, means to transmit said multichannel pulse wave, means to receive said multichannel pulse wave, and means to separate and demodulate said groups of pulses on said multichannel pulse wave to reproduce said signals.

3. The system of claim 2 wherein said means to interleave said groups of different pulse trains comprises an electronic distributor device having a plurality of targets, one for each signal channel, swept by a cathode ray beam.

4. The system of claim 2 wherein said means to interleave groups of different pulse trains comprises: a parallel grouping of electron discharge devices.

5. The system of claim 2 wherein said means to group in time a given number of pulses comprises a network of delay devices.

6. The system of claim 2 wherein means to separate and demodulate said groups of pulses includes a network of delay devices.

7. A multichannel communication system wherein each signal channel is modulated on a with the scanning separate train of pulses having the same pulserepetition rate comprising: separate cascades of self-restoring trigger circuits arranged to group in time a given number of said pulses on each train to produce trains of regularly recurring groups of pulses, and means to interleave said groups of different pulse trains with each other to form a multichannel pulse wave with the spacing between each of said groups exceeding the spacing of the pulses within each group.

8. The system of claim 7 wherein said trigger circuits are restored by a steady pulse wave synchronized with the repetition rate of the pulses on the trains introduced into said circuits.

9. In a multi-channel pulse communication system of the type in which a plurality of trains of pulses, each modulated in accordance with instantaneous values of the signal in a separate one of the plurality of signal channels, are transmitted substantially simultaneously; a cathode ray tube having beam producin means, beam deflecting means and a plurality of target elements arranged to be successively struck by the beam during its deflection, means for applying a group of succeeding pulses from one of said trains to a group of succeeding ones of said targets in synchronism with the impingement of the beam on said targets, means for applying another group of succeeding pulses from another one of said trains to a succeeding group of successive targets in synchronism with the impingement of the beam thereon, means associated with said targets and responsive to the impingement of the beam on any one of said targets for producing a pulsed current flow, thereby producing a multichannel pulse Wave output in which groups of pulses from each of said trains are interleaved with each other, and means to transmit said multi-channel pulse wave.

10. A multi-channel pulse communication system according to claim 9 wherein said target elements are dynodes, and the means associated with said target elements includes a collector.

11. A multi-channel pulse communication system according to claim 9 wherein the pulses of the aforesaid plurality of trains of pulses have a REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,624,596 Hartley Apr. 12, 1927 1,671,143 Campbell May 29, 1928 2,089,639 Bedford Aug. 10, 1937 2,105,016 Smith Jan. 11, 1938 2,146,876 Zworykin Feb. 14, 1939 2,172,354 Blumlein Sept. 12, 1939 2,191,565 Henroteau Feb. 27, 1940 2,199,634 Koch May 7, 1940 2,272,070 Reeves Feb. 3, 1942 2,277,516 Henroteau Mar. 24, 1942 2,406,165 Schroeder Aug. 20, 1946 2,408,077 Labin Sept. 24, 1946 FOREIGN PATENTS Number Country Date 259,328 Great Britain Oct. 14, 1926 587,941 Great Britain May 9, 1947 

